1. Field of the Invention
This invention relates to a failure determination system and method for an internal combustion engine and an engine control unit, and more particularly to a failure determination system and method and an engine control unit, for determining a failure of a variable valve mechanism which inactivates a valve system associated with at least one of cylinders during a predetermined operation of the engine.
2. Description of the Prior Art
Conventionally, a control system for an internal combustion engine has been disclosed e.g. in the publication of Japanese Patent No. 2507550. The control system is used for controlling the fuel supply and cut-off of the fuel supply depending on a misfire condition of the engine. More specifically, the control system detects a misfire condition, on a cylinder-by-cylinder basis, based on variation in the rotational speed of a crankshaft, and cuts off the supply of fuel to a cylinder in which a misfire has been determined to occur, for a predetermined time period. Further, after that, the supply of fuel to the cylinder is resumed, and it is detected again whether or not a misfire occurs, thereby preventing continuation of the state in which the misfire has been determined to occur and fuel supply is cut off, in spite of the fact that a misfire actually no longer occurs.
However, the conventional control system suffers from the following problems: Internal combustion engines include a type which has a variable valve mechanism for inactivating predetermined ones of cylinders during deceleration of the vehicle. The variable valve mechanism is configured such that it keeps an intake valve and an exhaust valve of each of the predetermined cylinders capable of opening and closing when these cylinders are allowed to operate, and on the other hand, when they are inhibited from operation, it holds the intake and exhaust valves in a state incapable of opening and closing. As a result, in the case of this kind of engine, if a failure of the variable valve mechanism has occurred, the intake and exhaust valves, which should open and close for operation of the cylinders as their inherent function, are sometimes held closed, causing misfires in these cylinders. However, in the conventional control system, since detection of a misfire is carried out only based on variation in the rotational speed of the crankshaft, it is impossible to determine whether the misfire occurs due to a failure of the variable valve mechanism or due to unstable combustion in the misfiring cylinder (normal misfire). This makes it impossible to properly cope with a misfire in a manner suited to the cause of the misfire.
It is an object of the invention to provide a failure determination system and method for an internal combustion engine and an engine control unit, which are capable of properly determining a failure of a variable valve mechanism by discriminating a misfire caused by the failure of the variable valve mechanism from a normal misfire.
To attain the above object, according to a first aspect of the present invention, there is provided a failure determination system for an internal combustion engine including a variable valve mechanism for inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine.
The failure determination system according to the first aspect of the invention is characterized by comprising:
cylinder-discriminating means for discriminating a particular one of the cylinders;
fuel injection valves for injecting fuel for the cylinders, on a cylinder-by-cylinder basis;
oxygen concentration-detecting means for detecting concentration of oxygen contained in exhaust gases exhausted from the engine;
misfire-detecting means for detecting a misfire condition of the engine, on a cylinder-by-cylinder basis;
fuel injection-stopping means for stopping fuel injection from the fuel injection valves to a cylinder of which occurrence of a misfire is detected by the misfire-detecting means; and
failure-determining means for determining that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection by the oxygen concentration-detecting means assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out by the fuel injection-stopping means.
According to this failure determination system, a misfire condition of the engine is detected on a cylinder-by-cylinder basis, and fuel injection to a cylinder of which occurrence of a misfire is detected by the misfire-detecting means via its associated fuel injection valve is stopped. When the oxygen concentration parameter determined based on results of the detection by the oxygen concentration-detecting means assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under the condition of the stoppage of fuel injection being carried out, it is judged that a failure of the variable valve mechanism has occurred. The variable valve mechanism, if normal, keeps the valve systems capable of opening and closing, when the engine is in an operating condition other than the predetermined condition. If the supply of fuel to a misfiring cylinder is cut off to supply only air to the cylinder, the oxygen concentration parameter responsive to oxygen concentration of exhaust gasses should indicate a leaner value of the air-fuel ratio of exhaust gases than when the fuel cut-off is not carried out, provided that the valve system is normally operating. Therefore, inversely, when the oxygen concentration parameter under the same conditions assumes a value indicating a richer value of the air-fuel ratio than a predetermined reference value does, it can be judged that the valve system of the misfiring cylinder is held closed and the variable valve mechanism is in a failure state in which it cannot control the valve system to a state capable of opening and closing. Further, in this case, the failure of the variable valve mechanism can be identified as the cause of the misfire, which makes it possible to clearly distinguish the misfire from a normal misfire.
Preferably, the fuel injection-stopping means cancels the stoppage of the fuel injection when the, oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does.
According to this preferred embodiment, when the oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does, i.e. when a misfire occurs due to some cause other than the failure of the variable valve mechanism, the stoppage of fuel injection is cancelled, whereby the engine can be properly and quickly restored to a state controlled to normal operation.
Preferably, the failure determination system includes engine rotational speed-detecting means for detecting a rotational speed of the engine, and the predetermined reference value is set such that the predetermined reference value indicates a richer value of the actual air-fuel ratio of the exhaust gases as the detected rotational speed of the engine is lower.
Preferably, the oxygen concentration parameter is an average value of a correction coefficient calculated in response to the detected oxygen concentration for use in air-fuel ratio feedback control of the engine.
Preferably, the failure determination system includes inhibition means for inhibiting the stoppage of the fuel injection by the fuel injection-stopping means and the determination by the failure-determining means, when a cylinder of which the occurrence of a misfire is detected does not belong to the at least one of the cylinders.
To attain the above object, according to a second aspect of the present invention, there is provided a failure determination system for an internal combustion engine including a variable valve mechanism for inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine.
The failure determination system according to the second aspect of the invention is characterized by comprising:
a cylinder-discriminating module for discriminating a particular one of the cylinders;
fuel injection valves for injecting fuel for the cylinders, on a cylinder-by-cylinder basis;
an oxygen concentration-detecting module for detecting concentration of oxygen contained in exhaust gases exhausted from the engine;
a misfire-detecting module for detecting a misfire condition of the engine, on a cylinder-by-cylinder basis;
a fuel injection-stopping module for stopping fuel injection from the fuel injection valves to a cylinder of which occurrence of a misfire is detected by the misfire-detecting module; and
a failure-determining module for determining that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection by the oxygen concentration-detecting module assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out by the fuel injection-stopping module.
According to the second aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the fuel injection-stopping module cancels the stoppage of the fuel injection when the oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the failure determination system includes an engine rotational speed-detecting module for detecting a rotational speed of the engine, and the predetermined reference value is set such that the predetermined reference value indicates a richer value of the actual air-fuel ratio of the exhaust gases as the detected rotational speed of the engine is lower.
Preferably, the failure determination system includes an inhibition module for inhibiting the stoppage of the fuel injection by the fuel injection-stopping module and the determination by the failure-determining module, when a cylinder of which the occurrence of a misfire is detected does not belong to the at least one of the cylinders.
To attain the above object, according to a third aspect of the present invention, there is provided a method of determining a failure of a variable valve mechanism of an internal combustion engine, the variable valve mechanism inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine.
The method according to the third aspect of the invention is characterized by comprising the steps of:
discriminating a particular one of the cylinders;
injecting fuel for the cylinders, on a cylinder-by-cylinder basis;
detecting concentration of oxygen contained in exhaust gases exhausted from the engine;
detecting a misfire condition of the engine, on a cylinder-by-cylinder basis;
stopping fuel injection from the fuel injection valves to a cylinder of which occurrence of a misfire is detected; and
determining that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection of oxygen concentration assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out.
According to the third aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the step of stopping fuel injection includes canceling the stoppage of the fuel injection when the oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the method includes the step of detecting a rotational speed of the engine, and the step of setting the predetermined reference value such that the predetermined reference value indicates a richer value of the actual air-fuel ratio of the exhaust gases as the detected rotational speed of the engine is lower.
Preferably, the method includes the step of inhibiting the stoppage of the fuel injection and the determination of failure of the variable valve mechanism, when a cylinder of which the occurrence of a misfire is detected does not belong to the at least one of the cylinders.
To attain the above object, according to a fourth aspect of the present invention, there is provided an engine control unit including a control program for causing a computer to determining a failure of a variable valve mechanism of an internal combustion engine, the variable valve mechanism inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine.
The engine control unit according to the fourth aspect of the invention is characterized in that the control program causes the computer to discriminate a particular one of the cylinders, inject fuel for the cylinders, on a cylinder-by-cylinder basis, detect concentration of oxygen contained in exhaust gases exhausted from the engine, detect a misfire condition of the engine, on a cylinder-by-cylinder basis, stop fuel injection from the fuel injection valves to a cylinder of which occurrence of a misfire is detected, and determine that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection of oxygen concentration assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out.
According to the fourth aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, in the case of the control program causing the computer to stop the fuel injection, the control program causes the computer to cancel the stoppage of the fuel injection when the oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control program causes the computer to detect a rotational speed of the engine, and set the predetermined reference value such that the predetermined reference value indicates a richer value of the actual air-fuel ratio of the exhaust gases as the detected rotational speed of the engine is lower.
Preferably, the control program causes the computer to inhibit the stoppage of the fuel injection and the determination of failure of the variable valve mechanism, when a cylinder of which the occurrence of a misfire is detected does not belong to the at least one of the cylinders.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.